There is no single, isolated cause of Alzheimer’s disease. Certain conditions, genetic markers and abnormal brain structures appear to predispose an individual to Alzheimer’s disease, but none of these have been clearly shown to be a cause of the disease. Due to this, researchers believe that Alzheimer’s is the result of a combination of risk factors, which may include:
- Genetic factors
- Head trauma
- Medical disorders.
Causes of Alzheimer’s Disease: Age and Gender
Although they are not “causes” of Alzheimer’s disease, age and gender are both considered fixed risk factors for developing the disease. Alzheimer’s symptoms do not generally appear before 60 years of age, and the risk of developing Alzheimer’s increases with age.
Women appear to be twice as likely as men to develop Alzheimer’s disease. This, however, may be a reflection of the fact that women, who typically live longer than men, are simply more likely to live long enough to develop Alzheimer’s disease.
Causes of Alzheimer’s Disease: Genetic Factors
Although Alzheimer’s can run in families, the majority of Alzheimer’s cases show no clear inheritance patterns. Inheritance patterns are much stronger in early-onset Alzheimer’s disease (onset prior to age 65).
The presence of a gene called Apolipoprotein E (ApoE) appears to increase the likelihood that an individual will develop late-onset Alzheimer’s disease. There are three forms of this gene: ApoE2, ApoE3 and ApoE4. The ApoE4 variant appears to cause Alzheimer’s in some cases. Here again, inheritance patterns are not clear, as not everyone who has this gene develops Alzheimer’s, and not everyone who develops Alzheimer’s has this gene.
Causes of Alzheimer’s Disease: Head Injuries
Head injuries can lead to brain damage, and brain damage can increase one’s risk of developing Alzheimer’s disease. Nevertheless, relatively few people with Alzheimer’s symptoms have suffered head trauma. Therefore, head injuries are only potential causes of Alzheimer’s disease in very few cases.
Causes of Alzheimer’s Disease: Medical Disorders
Hypertension (high blood pressure) and high cholesterol levels may indirectly increase the risk of Alzheimer’s disease by impairing blood flow to the brain (atherosclerosis). This can result in strokes and other forms of brain damage that may be a causal factor in Alzheimer’s disease.
The type 1 herpes simplex virus (HSV-1) that is responsible for cold sores around the mouth has also been linked to the ApoE4 gene. Therefore, individuals who experience periodic bouts of cold sores are more likely to possess the ApoE4 gene that makes them more susceptible to Alzheimer’s disease in their senior years.